Conventionally, as a ball for a ball game of an air sealing structure such as a soccer ball, a volleyball and a handball, there are two kinds of balls, i.e., a laminated ball and hand stitched ball.
(1) As described in U.S. Pat. No. 4,333,648 for example, the laminated ball is made of air-impermeable rubber, and comprises a spheral hollow rubber bladder into which air is charged through a valve, a reinforcing layer Formed by winding a some thousands meter long nylon filament around the rubber bladder in its every circumferential direction, a cover rubber comprising a vulcanized rubber thin layer covered on the reinforcing layer, and a skin panel adhered to the cover rubber.
A quality of the ball (weight, size, sphericity, durability, upkeep property in shape, and increased strength with respect of passage of time) is stabilized by the reinforcing layer.
The cover rubber functions to allow the skin panel to strongly adhere to the carcass.
An artificial skin or a natural skin panel is used as a material of the skin panel.
With the above-described structure, the laminated ball can be mechanically manufactured and therefore, productivity is high (variation in weight and size is small), price is low, and sphericity and durability are excellent due to the winding reinforcing layer, but there is a drawback that the ball is hard and if the ball hits a human body, it painfully hurts him or her. Further, since the ball is hard, there are problems that it is difficult to control the ball, and it is difficult to make use of a high technique.
The reason why the ball is hard is that absorption of impact when the ball is kicked only depends on elasticity of the nylon constituting the reinforcing layer.
(2) As described in U.S. Pat. No. 4,462,590 for example, the hand stitched ball comprises a bladder of the above-described laminated ball, and a surface skin layer formed by inwardly folding edges of a plurality of skin panels and sewing these edges into a spherical shape by a thread (thread of about 10,000 denier).
The bladder is accommodated in the surface skin layer. An artificial skin or a natural skin panel is used as the skin panel. Three to four cloths are adhered to the back surface of the artificial skin (which is called as a backing material). Sewing operation is carried out manually.
The hand stitched ball constituted in the above-described manner is soft, the ball feels good and thus is easy to play with, and it is easy to control the ball. On the other hand, however, since the ball is cubic, it can not be sewed by a sewing-machine and thus, it must be sewed manually. Therefore, there are problems that the hand stitched ball requires a skill for manufacture, the difference in skill among individuals is large, the productivity is poor, the cost is expensive, a quality (weight, variation in size, sphericity, durability and the like) is unstable, level of defectiveness is two to three times greater than that of the laminated ball, durability is inferior, and the ball is prone to be deformed.
When a ball receives an internal pressure of about 1.0 kg/cm.sup.2 and an impact by kicking or the like, an impact of some hundreds kg or more is applied to the ball. Therefore, there is an inconvenience that a seam of the ball may come apart, and a size of the ball may become larger than a standard or may be deformed. For this reason, there are problems that the thread may be cut due to the impact, a knot of the thread is untied and the bladder is exposed. Normally, durability of the hand stitched ball is one-half to one-third or less of that of the laminated ball.
A high control property of the hand stitched ball depends on the backing material (in the case of the skin panel, the backing material is included) of normally three to four layers backed on the back surface of the skin. The cloth has a corrugated structure in which the warp and the woof are crossed, and both the warp and the woof are woven from above and below with each other. The backing member has the same shape as that of the skin panel, and the backing member is independent for every skin panel. The cloth has a bias effect, and a function for absorbing the impact more effectively. The bias effect means an effect showing a large elasticity when the cloth is pulled in a direction inclined 45 degrees with respect to the warp and the woof. Therefore, the cloth has an excellent elasticity when it receives a shock.
Whereas, the nylon filament constituting the reinforcing layer of the laminated ball is not corrugated but is linear along the spherical surface, and is continuous. Therefore, impact absorbing performance is inferior.
From the above-described features, a highly skilled player uses the hand stitched ball in many cases, and the hand stitched ball is generally used for ball games. Whereas, the laminated ball is used in an elementary school or a junior high school, or is used for practice in many cases.
In order to improve the touch of the laminated ball, there has been proposed a structure in which a tape-like rubber is adhered only to a region of the winding reinforcing layer adjacent the skin panel, and only the edge portion of the skin panel is adhered to the rubber (Japanese Utility Model Registration No. 37647/1991). In this structure, however, the winding reinforcing layer exists, and the hardness due to this layer can not be moderated.
The present invention has been accomplished in view of such circumstances, and it is an object of the present invention to realize a ball having merits of these two kinds of balls, i.e., a ball having excellent productivity, durability, quality, and touch-feeling and which can easily be controlled.